Although death certificate data are limited by possible misdiagnosis, incomplete case ascertainment, errors in coding, etc., detailed morbidity information on neurologic diseases for the entire U.S. and for other countries is not available. The Section has analyzed mortality data for selected neurologic disorders by country and by county in the U.S. The overall patterns which emerge may be useful in evaluating trends over time and in formulating etiologic hypotheses. Some neurologic disease may contribute to death indirectly. Since there are no uniform criteria for what constitutes the underlying cause of death in patients, it is important to examine all deaths in which a disease is listed as an underlying, immediate, associated or contributory cause of death to get more complete information about the relationship between the disease and death. Mortality data for the U.S. for deaths due to and related to twenty neurologic diseases were studied. Diseases occurring together may provide important information in the search for etiology of diseases. Association of diseases occurring at the time of death was also studied for all deaths occurring in the U.S. from 1971 and 1973 through 1978.